Patent Literature 1 discloses a diesel engine capable of carrying out idling stop in which the diesel engine is automatically stopped during an idling operation. In the diesel engine of the conventional art, when shifting to an idling operation is carried out during execution of regeneration of a DPF by post injection, idling stop is prohibited until regeneration of the DPF is terminated, and regeneration of the DPF is continued during the idling operation. The reason therefor is that in a case where idling stop is carried out during regeneration of the DPF and regeneration of the DPF is interrupted, a remarkable drop of the temperature of the DPF is caused to thereby necessitate a prolonged time and large energy until regeneration of the DPF is terminated.